[Effect of trapidil and papaverine on thrombocyte aggregation and phosphodiesterase activity].

Trapidil effect on platelet aggregation in vitro and in vivo as well as on phosphodiesterase (PDE) activity was studied. Both ADP- and collagen-induced aggregation of human and rabbit platelets was inhibited by trapidil at concentrations of 60 mumol/l. The PDE activity of human platelet lysates was blocked at concentrations that were necessary to inhibit aggregation. Papaverine exerted 5 times higher inhibitory effects on aggregation and PDE activity as compared to trapidil. Infusion of trapidil to rabbits caused aggregation inhibition in vivo. Papaverine at equimolar doses was more effective than trapidil. At therapeutic doses trapidil is unlikely to produce adequate plasma levels for inhibition of platelet aggregation.